ELASTOMER BASED ON NICKEL ZINC FERRITE AND NATURAL RUBBER

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INVESTIGATION OF DYNAMIC MECHANICAL PROPERTIES OF MAGNETORHEOLOGICAL

ELASTOMER BASED ON NICKEL ZINC FERRITE AND NATURAL RUBBER

NUR HASLINA NASIRAH BINTI ABDUL HADI

UNIVERSITI SAINS MALAYSIA

2020

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INVESTIGATION OF DYNAMIC MECHANICAL PROPERTIES OF MAGNETORHEOLOGICAL

ELASTOMER BASED ON NICKEL ZINC FERRITE AND NATURAL RUBBER

by

NUR HASLINA NASIRAH BINTI ABDUL HADI

Thesis submitted in fulfilment of the requirements for the degree of

Master of Science

February 2020

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ACKNOWLEDGEMENT

In the name of Allah SWT, the most gracious and most merciful who created the world for giving me this blessing, that I can finish conducting my research project through every difficulty and has helped me complete this dissertation with ease. Shalawat and Salam are upon Muhammad S.A.W who brought peaceful in the world.

I would like to express my sincere appreciation to my supervisor, Dr Raa Khimi Shuib for his invaluable guidance throughout completing this research and for his generosity in sharing knowledge and keep motivating me throughout this journey.

Apart from that, I would like to acknowledge my co-supervisor, Dr Muhammad Khalil Abdullah for providing information and support in order to complete this thesis.

I would also like to thank the Dean and all of the staff in School of Materials and Mineral Resources Engineering USM for their diligent assistance throughout the duration of my research, especially Mr. Suharudin Sulong and Mr. Shahril Amir for offering their time, technical aid and insights.

Many thanks to my research partners and all my friends for their help, support, prayer and encouragement that inspired me a lot to complete my research study.

Furthermore, my deepest gratitude goes out to both of my parents, Abdul Hadi Bin Muhammad and Shariah Binti Mohammad and my sisters for their prayer, moral and financial support. Their support was invaluable and assists me to conquer any difficulties in completing my research project.

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TABLE OF CONTENTS

ACKNOWLEDGEMENT ... ii

TABLE OF CONTENTS ... iii

LIST OF TABLES ... viii

LIST OF FIGURES ... ix

LIST OF SYMBOLS ... xiii

LIST OF ABBREVIATIONS ... xiv

ABSTRAK ... xv

ABSTRACT ... xvii

CHAPTER 1 INTRODUCTION... 1

1.1 Background of study ... 1

1.2 Problem statement ... 3

1.3 Research objectives ... 6

1.4 Outline of the thesis ... 6

1.5 Scope of study ... 7

CHAPTER 2 LITERATURE REVIEW ... 8

2.1 Magnetorheological (MR) materials ... 8

2.1.1 Magnetorheological fluids (MRFs) ... 8

2.1.2 Magnetorheological elastomers (MREs) ... 10

2.2 Damping mechanisms in magnetorheological elastomers ... 11

2.2.1 Viscoelastic damping ... 11

2.2.2 Interfacial damping ... 12

2.2.3 Magnetism-induced damping ... 13

2.3 Magnetorheological elastomer applications ... 14

2.4 Magnetorheological elastomer components ... 16

2.4.1 Matrix material ... 16 Page

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2.4.1(a) Natural rubber ... 18

2.4.1(b) Rubber compounding ingredients ... 22

2.4.2 Magnetic particles ... 23

2.5 Fabrication process of magnetorheological elastomers... 28

2.5.1 Mixing ... 28

2.5.1 Vulcanization and measurement of cure characteristics ... 29

2.5.3 Shaping and curing for magnetorheological elastomers (MREs) ... 32

2.6 Factors affecting magnetorheological elastomer performance ... 36

2.6.1 Viscosity of rubber matrix ... 36

2.6.2 Surface modification of magnetic particles ... 37

2.6.3 Magnetic field strength ... 40

2.6.4 Other factors ... 40

CHAPTER 3 METHODOLOGY ... 42

3.1 Introduction ... 42

3.2 Materials ... 43

3.2.1 Rubber matrix ... 44

3.2.2 Zinc oxide and stearic acid ... 44

3.2.3 Nickel zinc ferrite ... 44

3.2.4 Paraffin oil ... 45

3.2.5 N-cyclohexyl-2-benzothyazolsulfenamide (CBS) ... 45

3.2.6 Tetra-methylthiuram disulphide (TMTD) ... 45

3.2.7 N-isopropyl-n'-phenyl-p-phenylenediamine (IPPD) ... 46

3.2.8 Bis [3-(triethoxysilyl) propyl] tetrasulfide (TESPT) ... 46

3.2.9 Sulphur... 46

3.2.10 Toluene ... 46

3.3 Equipment ... 47

3.4 Formulation and preparation of magnetorheological elastomer (MREs) ... 48

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3.4.1 Preparation of nickel zinc ferrite ... 48

3.4.2 Preparation of MREs with different matrix viscosity ... 48

3.4.3 Preparation of MREs with different content of TESPT and matrix viscosity ... 49

3.4.4 Surface treatment of nickel zinc ferrite ... 50

3.4.5 Preparation of MREs with different magnetic field ... 51

3.4.6 Rubber compounding ... 51

3.4.7 Measurement of cure characteristics ... 53

3.4.8 Vulcanization process ... 53

3.5 Materials characterization ... 55

3.5.1 Particle size ... 55

3.5.2 Magnetic properties ... 55

3.5.3 Fourier Transform Infrared Spectroscopy ... 56

3.5.4 Thermal gravimetric analysis (TGA) ... 56

3.5.5 Swelling and crosslink density ... 57

3.5.6 Tensile test ... 58

3.5.7 Dynamic mechanical properties ... 58

3.5.8 Morphology test ... 59

CHAPTER 4 RESULTS ANALYSIS AND DISCUSSION ... 60

4.1 Characterization of waste nickel zinc ferrite ... 60

4.2 Matrix viscosity of magnetorheological elastomers ... 62

4.3 Influence of matrix viscosity on the dynamic mechanical performance of magnetorheological elastomers ... 63

4.3.1 Scanning electron microscope (SEM) ... 63

4.3.2 Curing characteristic ... 66

4.3.3(a) Frequency sweep measurement ... 70

4.3.3(b) Strain amplitude measurement ... 73

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4.3.4 Tensile properties ... 76

4.3.4(a) Tensile strength... 76

4.3.4(b) Elongation at break ... 77

4.3.4(c) Modulus at 100% elongation (M100) ... 78

4.3.5 Glass transition temperature (Tg) ... 79

4.3.6 Thermogravimetric analysis (TGA) ... 80

4.4 Effect of silane coupling agent on dynamic mechanical performance of plasticized anisotropic magnetorheological elastomers ... 82

4.4.1 Characterization of surface modified nickel zinc ferrite particles .... 82

4.4.2 Curing characterization of MREs ... 89

4.4.3 Morphology ... 91

4.5 Effect of magnetic field on dynamic mechanical properties of magnetorheological elastomers ... 103

4.5.1 Morphology ... 103

4.5.3 Glass Transition Temperature (Tg) ... 111

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CHAPTER 5 CONCLUSION AND FUTURE RECOMMENDATIONS .... 116

5.1 Conclusion ... 116 5.1.1 To characterize the properties of waste nickel zinc ferrite ... 116 5.1.2 To assess the effect of matrix viscosity on the formation of magnetic

particle alignment in magnetorheological elastomers (MREs) ... 116 5.1.3 To evaluate the role of interfacial damping through weakly bonded

interfaces and strongly bonded interfaces between nickel zinc ferrite particle and natural rubber matrix ... 117 5.1.4 To investigate the effect of magnetic field on magnetic particle

interaction and dynamic mechanical performance of MREs ... 117 5.2 Recommendations for future works ... 119 REFERENCES ... 120 LIST OF PUBLICATIONS

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LIST OF TABLES

Table 2.1 List of matrix types commonly used in MREs... 17

Table 2.2 Physical properties of common types of rubber ... 18

Table 2.3 Chemical composition of fresh latex ... 20

Table 2.4 Specifications for natural rubber grades ... 21

Table 2.5 Common additives used in rubber compounding... 22

Table 2.6 List of particle types commonly used in MREs ... 26

Table 2.7 Methods of common surface modification used ... 38

Table 3.1 List of materials with their manufacturers and commercial names ... 43

Table 3.2 Properties of SMR L ... 44

Table 3.3 List of equipment ... 47

Table 3.4 Formulation of MREs with different matrix viscosity ... 48

Table 3.5 Formulation of MREs with different content of TESPT and matrix viscosity ... 50

Table 3.6 Formulation of MREs with different magnetic field... 51

Table 3.7 The mixing sequence of rubber compounding ... 52

Table 4.1 Elemental composition of nickel zinc ferrite particles ... 61

Table 4.2 VSM data of nickel zinc ferrite particle ... 61

Table 4.3 Viscosity of Anisotropic MREs with different plasticizer contents... 63 Page

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LIST OF FIGURES

Page Figure 2.1 MRF structure; (a) in the absence of magnetic field and (b) under

influence of magnetic field ... 9

Figure 2.2 Cyclic stress-strain viscoelastic curve split up into viscous and elastic components ... 12

Figure 2.3 Constrained and free rubber in an agglomerate ... 13

Figure 2.4 Prototype of (a) tuned vibration absorption system using MRE, (b) MRE isolator with variable stiffness and damping, (c) MRE-based force sensor and (d) tuneable spring element ... 16

Figure 2.5 Structure of linear poly(cis-1,4-isoprene) ... 19

Figure 2.6 Mapping of MREs based on magnetizable particle; (a) based on particle size, (b) based on particle shape ... 24

Figure 2.7 Waste nickel zinc ferrite particles ... 27

Figure 2.8 MREs fabrication process ... 28

Figure 2.9 Two roll mill ... 29

Figure 2.10 Sulphur vulcanisation of cis-polyisoprene ... 31

Figure 2.11 Schematic diagram of compression moulding ... 34

Figure 2.12 Magnet mould for MRE fabrication. ... 34

Figure 2.13 Electromagnetic-heat coupled device for MRE fabrication. ... 35

Figure 3.1 The flow chart of research methodology ... 43

Figure 3.2 Molecular structure of TESPT ... 46

Figure 3.3 Permanent magnet magnetic mould for anisotropic curing ... 54

Figure 3.4 Electronic magnetometer ... 55

Figure 4.1 SEM micrograph of nickel zinc ferrite particles ... 60

Figure 4.2 Particle size distribution of nickel zinc ferrite ... 61

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Figure 4.3 Storage modulus versus strain to define the LVE region ... 62

Figure 4.4 Loss modulus versus strain to define the LVE region ... 62

Figure 4.5 SEM images of the MREs at different matrix viscosity, a) MV1, b) MV2, c) MV3, d) MV4, e) MV5 and f) MV6... 65

Figure 4.6 Thickness and length of waste nickel zinc ferrite chains at different matrix viscosity ... 66

Figure 4.7 (a) scorch and cure time at different matrix viscosity (b) Torque different at different matrix viscosity ... 68

Figure 4.8 Crosslink density of anisotropic MREs at different matrix viscosity ... 69

Figure 4.9 Shear stress of anisotropic MREs at different matrix viscosity ... 69

Figure 4.10 Tan δ (a) storage modulus (b) and loss modulus (c) of MREs with different matrix viscosity against frequency. ... 73

Figure 4.11 Tan δ (a) storage modulus (b) and loss modulus (c) of MREs with different matrix viscosity against strain amplitude. ... 75

Figure 4.12 Tensile strength of MREs at different matrix viscosity ... 77

Figure 4.13 Elongation at break of MREs at different matrix viscosity... 78

Figure 4.14 Modulus (M100) at different matrix viscosity ... 79

Figure 4.15 Tan δ at different matrix viscosity ... 80

Figure 4.16 TGA curves of MREs with different matrix viscosity in the nitrogen ... 81

Figure 4.17 Schematic illustration of the reactions of TESPT with waste nickel zinc ferrite particles ... 83

Figure 4.18 FTIR spectra of waste nickel zinc ferrite particles at different TESPT contents ... 84

Figure 4.19 TGA curves for waste nickel zinc ferrite particles at different TESPT contents ... 85

Figure 4.20 Silane grafting percentage of waste nickel zinc ferrite at different TESPT contents ... 86

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Figure 4.21 Schematic diagram of formation of polymeric siloxane oligomer... 86 Figure 4.22 Schematic illustration of the reaction mechanisms of tetrasulphane

group of TESPT with the natural rubber ... 88 Figure 4.23 Crosslink density of MREs with different TESPT ... 89 Figure 4.24 Scorch and cure time for MRE/LV and MRE/HV with different

contents of TESPT ... 90 Figure 4.25 Torque different for MRE/LV and MRE/HV at different TESPT

content ... 91 Figure 4.26 SEM images of fracture of MREs with (a) unmodified and (b)

modified waste nickel zinc ferrite (treated with 6 phr of TESPT) ... 92 Figure 4.27 SEM images of fracture (a) MRE/LV and (b) MRE/HV ... 93 Figure 4.28 (a)Tan δ of MRE/HV (b) Tan δ of MRE/LV (c) Storage modulus

(G′) of MRE/HV (d) Storage modulus (G′) of MRE/LV(e) Loss modulus (G″) of MRE/HV (f) Loss modulus (G″) of MRE/LV vs.

frequency with different TESPT contents ... 95 Figure 4.29 (a)Tan δ of MRE/HV (b) Tan δ of MRE/LV (c) Storage modulus

(G′) of MRE/HV (d) Storage modulus (G′) of MRE/LV(e) Loss modulus (G″) of MRE/HV (f) Loss modulus (G″) of MRE/LV vs.

strain amplitude with different TESPT contents ... 98 Figure 4.30 Tensile strength of MRE/LV and MRE/HV at different TESPT

content ... 100 Figure 4.31 Elongation at break of MRE/HV and MRE/LV at different TESPT

content ... 101 Figure 4.32 Modulus M100 of MRE/HV and MRE/LV at different TESPT

content ... 102 Figure 4.33 SEM images of fractured surface at different magnetic field; (a) 0

mT, (b) 100 mT, (c) 150 mT, (d) 165 mT and (e) 200 mT. ... 104 Figure 4.34 Swelling percentage of MREs at different magnetic field ... 105 Figure 4.35 (a) Tan δ (b) Storage modulus (c) Loss modulus versus frequency

for MREs at different magnetic field ... 108

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Figure 4.36 (a) Tan δ (b) Storage modulus (c) Loss modulus versus frequency for MREs at different magnetic field ... 110 Figure 4.37 Tan δ of MREs at different magnetic field ... 111 Figure 4.38 Tensile strength of MREs at different magnetic field ... 113 Figure 4.39 Comparison of loading modes on particle separation, (a) tensile

mode, (b) shear mode ... 113 Figure 4.40 Elongation at break of MREs at different magnetic field ... 114 Figure 4.41 Modulus (M100) of MREs at different magnetic field ... 115

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LIST OF SYMBOLS

G' Storage modulus

G" Loss modulus

Hc Coercive force

mT Militesla

mdry Dry mass of MREs

mwet Swollen equilibrium mass M1 Original mass of MREs rubber

M2 MREs rubber swollen mass

MH Maximum torque

ML Minimum torque

Ms Saturation magnetization

Mr Remanence

ts2 Scorch time

t90 Cure time

tan δ Tan delta

Tg Glass transition temperature Vo Molar volume of toluene

Vp Volume fraction of the particles

Vr Volume fraction of MREs

ρr Density of natural rubber

ρs Density of toluene

X Interaction parameter between rubber and toluene

δ Phase angle

[χ] Crosslink density

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LIST OF ABBREVIATIONS

APTES (3-aminopropyl) triethoxy silane

ASTM American Society of Testing and Materials

BR Butadiene rubber

CBS N-cyclohexyl-2-benzothyazolsulfenamide DMA Dynamic Mechanical Analysis

DOP Dioctyl Phthalate

DPG Diphenyl guanidine

EP Epoxy resin

FESEM Fourier emission scanning electron microscope FTIR Fourier Transform Infrared Spectoscopy IPPD N-isopropyl-n'-phenyl-p-phenylenediamine ISO International Standards Organisations LVE Linear viscoelastic

MBT Mercaptobenzothiazole

MR Magnetorheological

MREs Magnetorheological elastomers MRFs Magnetorheological fluids M100 Modulus at 100% elongation

PANI Polyaniline

phr Parts per hundred rubber

PU Polyurethane

SEM Scanning Electron Microscope SMR Standard Malaysian Rubber

TESPT Bis [3-(triethoxysilyl)propyl] tetrasulfide TGA Thermal gravimetric analysis

TMTD Tetra-methylthiuram disulphide TSR Technically Specified Rubber VSM Vibrating sample magnetometer

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PENYIASATAN SIFAT MEKANIK DINAMIK ELASTOMER MAGNETOREOLOGI BERDASARKAN NIKEL ZINK FERIT DAN GETAH

ASLI

ABSTRAK

Elastomer magnetorheologi (MREs) adalah kelas komposit yang terdiri daripada matrik elastomerik dengan partikel magnet tertanam. Prestasi MREs dipengaruhi oleh sifat viskoelastik matrik getah, interaksi antara muka partikel magnet dan matrik getah dan mekanisme tambahan melalui interaksi partikel magnet. Dalam kajian ini, MREs berasaskan getah asli dan sisa nikel ferit telah dihasilkan. Komponen individu dalam MREs yang mempengaruhi prestasi dan penyerapan tenaga bahan tersebut telah disiasat. MREs dengan kelikatan matrik getah yang berbeza dan sisa industri nikel zink ferit telah disediakan untuk mengkaji kesan sifat viskoelastik matrik getah kepada prestasi dinamik dan mekanikal. Hasil dari kajian ini menunjukkan bahawa, tan δ meningkat dengan peningkatan kelikatan matrik dalam julat frekuensi dan amplitud ketegangan yang diuji. Kajian ini juga mendapati kekuatan dan pemanjangan tegangan pada rehat meningkat dengan peningkatan kelikatan matrik.

Mikrograf pengimbas mikroskop elektron (SEM) menunjukkan bahawa struktur kolumnar menjadi lebih panjang dan tebal dengan penurunan kelikatan matrik. Walau bagaimanapun banyak rongga kekal terhasil daripada partikel magnet yang terkeluar menunjukkan bahawa interaksi yang lemah antara sisa nikel zink ferit dan matrik getah. Untuk menilai kesan interaksi antara partikel magnet dan matrik getah terhadap prestasi dinamik dan mekanikal MREs, bis [3- (triethoxysilyl) propil] tetrasulfida (TESPT) telah digunakan untuk mengubah permukaan nikel zink ferit. Kandungan TESPT diubah pada 0, 2, 4, 6 dan 8% untuk kelikatan matrik getah yang rendah dan

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tinggi. Ikatan antara muka yang lebih baik telah dibuktikan oleh spektroskopi Fourier infra-merah (FTIR), peratusan ikatan cantuman, kepadatan sambung silang dan gambar SEM. Hasilnya menunjukkan bahawa tan δ meningkat lebih kurang 30% untuk julat frekuensi dan amplitud tegangan diuji untuk kelikatan matrik getah rendah dan tinggi. Interaksi yang lebih baik juga meningkatkan sifat tegangan MREs dan kandungan optimum TESPT didapati pada 6 wt%. Kesan interaksi antara partikel magnet terhadap prestasi dinamik dan mekanik MREs telah disiasat dengan pemvulkanan bahan pada medan magnet 0, 100, 150, 165 dan 200 mT. Hasilnya menunjukkan bahawa tan δ meningkat apabila medan magnet meningkat dan kekal di titik ketepuan magnet pada 165 mT. Walau bagaimanapun, kekuatan tegangan didapati menurun dengan medan magnet yang semakin meningkat disebabkan oleh arah beban tegangan berserenjang dengan penjajaran partikel magnet.

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INVESTIGATION OF DYNAMIC MECHANICAL PROPERTIES OF MAGNETORHEOLOGICAL ELASTOMER BASED ON NICKEL ZINC

FERRITE AND NATURAL RUBBER

ABSTRACT

Magnetorheological elastomers (MREs) are a class of composite that consist of elastomeric matrix with embedded magnetic particles. The performance of MREs can be ascribed to viscoelastic properties of rubber matrix, interfacial interaction at the interface between the rubber matrix and magnetic particles as well as additional mechanism through interparticle magnetic particle interaction. In this research, MREs based on natural rubber and waste nickel zinc ferrites were prepared. Individual components in MREs that contribute to the performance and energy absorption of the materials were investigated. MREs with different natural rubber matrix viscosities and industrial waste nickel zinc ferrite were prepared in order to study the effect of viscoelastic properties of rubber matrix on the dynamic and mechanical performance of the materials. The results revealed that the tan δ increased with increasing matrix viscosity over the whole range of frequency and strain amplitude explored. It was also found that the tensile strength and elongation at break increased with increasing matrix viscosity. The scanning electron microscope (SEM) micrographs revealed that the columnar structures became longer and thicker with a decrease in matrix viscosity.

However, numerous cavities remained due to particle pull out, suggesting poor interaction between waste nickel zinc ferrite and rubber matrix. For assessing the effect of interfacial interaction between rubber matrix and magnetic particles on dynamic and mechanical performance of the MREs, Bis-(3-triethoxysilylpropyl) tetrasulphane (TESPT) was utilized to modify the surface of nickel zinc ferrite. The content of

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TESPT was varied at 0, 2, 4, 6, and 8 wt% for the low and high viscosity rubber matrix.

The improved interfacial bonding was evidenced by Fourier transform infrared spectroscopy (FTIR), grafting percentage, crosslink density and SEM images. The result revealed that the tan δ improved approximately 30% over the frequency and strain amplitude explored for both low and high viscosity rubber matrix. Stronger interfacial interaction also improved the tensile properties of the MREs and the optimum content of TESPT was found to be at 6 wt%. The effect of interparticle magnetic particle interaction on dynamic and mechanical performance of the MREs was investigated by curing the materials at 0, 100, 150, 165 and 200 mT magnetic field. It was found that the tan δ increased as the magnetic field increased and level off at magnetic saturation point of 165 mT. However, the tensile strength was found to decrease with increasing magnetic field due to the tensile load direction is perpendicular to the magnetic particles alignment.

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1 CHAPTER 1 INTRODUCTION

1.1 Background of study

Magnetorheological elastomer (MRE) is a class of composite material that consists of magnetic particles suspended within an elastomer matrix. The magnetic particles used in MRE are carbonyl iron, iron oxides and other soft-magnetic particles without magnetic hysteresis, and suitable elastomer matrix materials include natural rubber (Yoon et al., 2013), silicone rubber (Shiga et al., 1995), nitrile rubber (Tian et al., 2013), polybutadiene rubber (Fuchs et al., 2007) and polyurethane rubber (Ju et al., 2016). MREs could be constructed as isotropic and anisotropic MREs (Zhou, 2003, Boczkowska et al., 2012). The isotropic MRE is characterized by its homogeneous dispersion of magnetic particles in a natural rubber matrix. The anisotropic MRE formed chain-like magnetic particle structures within a rubber matrix as a result of subjecting the material to an external magnetic field during curing (Farshad and Benine, 2004). Formation of such chain-like structures relies on the mechanism such that when individual particles are exposed to an applied magnetic field, magnetic dipole moments pointing along the field direction are induced within them. A magnetic force will cause the north pole of one particle to attract the south pole of its neighbour, resulting in the formation of chains and columnar structures inside the matrix (Shuib, 2015, Shuib and Pickering, 2016).

Eventually, when the matrix is cured, the particle structure set in place.

Anisotropic MRE is found to produce materials with larger stiffness and better damping performance compared to isotropic MRE or conventional rubber composites (Ginder et al., 1999). Here damping is mainly promoted by energy absorption by friction between the molecule chains in the rubber matrix and damping provided by

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matrix-filler interface as with conventional rubber composites, but inclusion of magnetic particles in rubber enables additional damping through magnetism-induced damping (Kaleta et al., 2011). Jung et al. (2016) investigated the MR performance of isotropic and anisotropic MRE systems prepared using natural rubber (NR) and carbonyl iron (CI) particles and found that the anisotropic MRE possessed a larger storage modulus than the isotropic one, which was explained as due to the reason that the chain-like structure formed by aligned particles along the field direction acts as a rod-like filler. Similarly, Lu et al. (2012) reported that for MRE consisting of thermoplastic poly (styrene-b-ethylene-co-butylene-b-styrene) rubber and CI particles, the anisotropic MRE showed an even higher initial storage modulus because the filler effect resulting from the chain-like structure of the particles enhanced the magnetic permeability of the MRE.

MREs hold promise in a large variety of engineering fields for vibration control and vibration isolation systems, including the automotive industry (Cao and Deng, 2009), machinery (Xu et al., 2010) and earthquake resistance (Yang et al., 2016). The formation of columnar structures in anisotropic MREs has huge potential implication to practical applications. For instance, current seismic bearings are large and heavy which typically consists of rubber-reinforced metal plates installed for a mid-sized building. In order to apply the technology of seismic isolation for public housing and low cost buildings, columnar structures of anisotropic MREs provide micro reinforcement to the rubber matrix and offer huge potential to be applied as seismic bearing. Dyke et al. (1996) investigated the performance of a semiactive control system-based newly developed magnetorheological fluid (MRF) dampers. Khimi and Pickering, (2015) compared the performance of anisotropic MREs with conventional antivibration rubber for potential application in vibration damping. The results

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revealed the performance of MREs were comparable with conventional antivibration rubber.

1.2 Problem statement

The most commonly used rubber matrix for MREs is natural rubber (Yoon et al., 2013, Chung et al., 2015) and synthetic rubbers such as silicone rubber (Shiga et al., 1995, Sedlacik et al., 2016, Perales-Martínez et al., 2017), nitrile rubber (Tian et al., 2013), and polyurethane rubber (Chokkalingam et al., 2011, Ju et al., 2016).

Natural rubber is preferred matrix, because it has good elasticity and damping properties. Furthermore, natural rubber does not corrode and is able to withstand abrasive substances such as salt water, acids, and corrosive liquids (Le Gac et al., 2015, Chandrasekaran, 2010). It can also bond well to metal parts and is relatively easy to process. The most magnetic particles for MREs are carbonyl iron and iron oxides (Jang et al., 2005). Carbonyl iron is frequently used due to their high magnetization (up to 2.1 Tesla), low residual magnetization, high magnetic permeability and soft magnetic characteristics. However, the price of carbonyl iron particles is too high, at

$13─$20/kg in bulk (Goodman, 2019).

In order to reduce the cost of MREs, waste nickel zinc ferrite was selected in this study as the magnetic particles. Waste nickel zinc ferrite has a number of advantages including high magnetic permeability, high electrical resistivity, good chemical stability, and low cost (Mathew and Juang, 2007). It is a product of the excess raw material from ferrite industries, which manufacture electronic inductors, power transformer cores, antennas, and transponders. These industries generate 3─10 tonnes of waste nickel zinc ferrite per month (Hossen et al., 2015). The waste nickel zinc ferrite from manufacturing is usually abandoned although it contains 70% ferrite. The

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waste also cannot be recycled because of its complex compositions (Ismail et al., 2007). Inorganic impurities might also be present on the surface of the nickel zinc ferrite which is generated during the cutting and machining process (Pereira et al., 1999). Furthermore, the waste nickel zinc ferrite contains heavy metal elements such as zinc and nickel, which could harm health of the human and the environment if not treated properly prior to disposal (Kmita et al., 2016). The introduction of waste nickel zinc ferrite used in MREs is one of the interesting perspectives that could lead to a more sustainable environment, recycling and profit earning.

The fabrication of MREs requires in-depth consideration, not only the selection of the magnetic particles and the type of rubber matrix, but also depends on matrix viscosity. The matrix viscosity of MREs is believed to significantly impact the abilities of the magnetic particles to orientate along the magnetic field direction during curing, which, in turn, affect the structural formation of columnar structure within anisotropic MREs (Oh et al., 2014). Therefore, it is sensible to optimize the matrix viscosity of MREs to improve the formation of columnar structures in MREs, which could possibly increase the dynamic mechanical performance of the materials through magnetic particle interactions.

Development of MREs based on industrial nickel zinc ferrite and natural rubber in this work sets a challenge as the inorganic magnetic fillers are inherently incompatible with organic rubber matrix which leads to poor adhesion and wettability between the rubber matrix and magnetic filler. Therefore, surface modification of nickel zinc ferrite magnetic fillers is an attractive approach in order to promote adhesion and enhance the dispersion of magnetic fillers within the rubber matrix to ensure that the production of final product having high performance.

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Surface modification of inorganic particles nickel zinc ferrite was employed by bifunctional coupling agent treatment. This treatment uses silane based coupling agent, which is the most effective and low cost treatment. Silane based coupling agent are silicon-based chemicals which consist of hydrolysable groups (for example methoxy, acetoxy or ethoxy) at one end that react with inorganic materials and organofunctional groups (for example amino or sulphide) at the other end which can react with the rubber matrix. Thus, it is expected that the silane coupling agent can couple the inorganic and organic materials and improve compatibility and interfacial interaction of MREs.

Additional important feature that affect the damping performance of MRE is applied magnetic field during curing. Magnetism-induced damping in MREs possibly due to increased energy absorbed to defeat interparticle magnetic interaction between neighbouring particles. The highest possible increase in damping between magnetic particle interactions occurs when the aligned particles develop magnetically saturated.

Chen et al. (2007) stated that for MREs based on natural rubber having 60 wt%

carbonyl iron particles, saturation happened around 400 mT and Qiao et al. (2012) also mentioned for MREs based on thermoplastic elastomer matrix having modified carbonyl iron, the saturation happened at around 500 mT. The results also revealed that, more particles combined each other and the chain like columnar structures became thicker and longer as the magnetic field strength increased to provide much larger damping. However, none has assessed the magnetic saturation for nickel zinc ferrite embedded in natural rubber matrix. Therefore, a substantial study on magnetism induced damping provided by waste nickel zinc ferrite particles in natural rubber based MREs is essential in order to understand the relative importance of this mechanisms in magnetorheological elastomers (MREs).